Just Say No Rated 1 out of 5 stars

Good idea. Poor implementation.Seemed to work at first. Then I changed calendars and Thunderbird froze. And yes, with this app installed, week numbering does disappear. For what it provides (a year in review) and what it takes away, not worth the bother.

This review is for a previous version of the add-on (0.4.0). 

As I've written already, this extension in veeeery slow to redraw. It's like drawing 12 month views. If you want to see a lot of calendars with a lot of events, it could take a long time...
For the week numbers: I can't understand. I'm using it on TB 6.0 wiht lightning 1.0b5 and it shows up like you can see in screenshots.
If you could provide more information on your setup and what is missing I could try to fix it :) You can use the "support email" or the github's issues system.
Thank you!